1. Field of the Invention
This invention relates to a medicament intermediate and method for preparing the same, and more particularly to a rosuvastatin calcium intermediate and method for preparing the same.
2. Description of the Related Art
Rosuvastatin calcium, with chemical name of (+)-(3R,5S)-7-[4-(4-fluorophenyl)-6-isopropyl-2-(N-methyl-N-mesyl amino)pyrimidine-5-yl]-3,5-dihydroxyl-6(E)-heptenoic acid calcium (2:1), is used for auxiliary treatment of patients with primary hypercholesterolemia (IIa type, including heterozygous familial hypercholesterolemia) or combined hyperlipidemia (IIb type) when diet or exercise therapy is not ideal. Rosuvastatin calcium can lower rising LDL-cholesterol, total cholesterol, triglyceride, and ApoB, and increase HDL-cholesterol. Rosuvastatin calcium also applies to the patients with homozygous familial hypercholesterolemia, and can be used alone or used in combination with a dieting or other blood-fat depressing methods (e.g. LDL apheresis). Because of its advantages of high efficiency, low toxicity, and small side effect, rosuvastatin calcium is popular and has a broad application prospect. Its chemical structural formula is as follows:

Methyl (3R)-3-(tert-butyldimethylsilyloxy)-5-oxo-6-triphenylphosphoranylidene hexanoate described in the invention is an important intermediate for preparing rosuvastatin calcium.
A typical method for preparing methyl (3R)-3-(tert-butyldimethylsilyloxy)-5-oxo-6-triphenylphosphoranylidene hexanoate by taking (3R)-3-(tent-butyldimethylsilyl)oxypentanedioate-1-methyl monoester as a raw material is described as follows:
wherein, Y represents a carboxyl protecting group, TBS represents tert-butyldimethylsilyl, and Ph represents phenyl. In the method, the carboxyl protecting group Y must be a large group, so as to enhance the stability of the protected ester group and improve the selectivity of monomethyl ester hydrolysis in the first step reaction. If the carboxyl protecting group Y is a small group, for example, methyl, the difficulty in hydrolysis of monomethyl ester will be increased greatly, and the yield of the monomethyl ester hydrolysate is low and even fails to obtain. Therefore, the method is high in preparation cost and not suitable for large-scale industrial production.
Another conventional method for preparing methyl (3R)-3-(tert-butyldimethylsilyloxy)-5-oxo-6-triphenylphosphoranylidene hexanoate by taking an acid anhydride compound as a raw material is given below:

In the method, the used raw material acid anhydride compound is high in price, the yield of the product in the first step reaction is low, and the problem of high preparation cost also exists, therefore, the method is not suitable for large-scale industrial production.